The present invention relates to stable, aqueous insulin formulations without phenol and m-cresol suitable for pulmonary delivery and for delivery when phenol and m-cresol are undesirable, providing increased convenience for the patient.
Diabetes is a general term for disorders in man having excessive urine excretion as in diabetes mellitus and diabetes insipidus. Diabetes mellitus is a metabolic disorder in which the ability to utilize glucose is more or less completely lost. About 2% of all people suffer from diabetes.
Since the introduction of insulin in the 1920""s, continuous strides have been made to improve the treatment of diabetes mellitus. To help avoid extreme glycaemia levels, diabetic patients often practice multiple injection therapy, whereby insulin is administered with each meal.
In solution, the self-association pattern of insulin is a complex function of protein concentration, metal ions, pH, ionic strength and solvent composition. For the currently used soluble preparations containing U100 insulin, zinc ions, isotonic agent and phenolic preservative, the following equilibria must be considered:
6In⇄3In2
3In2+2Zn2+⇄In6(T6)
T6⇄T3R3⇄R6
The known degradation patterns of insulin include a) fibril formation; b) deamidations at A18, A21 and B3; c) dimerisations via transamidation or Schiff-base formation; d) disulfide exchange reactions.
According to Brange (Stability of Insulin, Kluwer Academic Press,1994), each of these degradation reactions proceed much faster in the monomeric state than in the hexameric state. Therefore, the most efficient means of stabilising insulin preparations is by pushing the above equilibrium as far to the right as possible. In addition to this general effect of mass action, the reactivity of selected residues is further modified depending on their direct involvement in the Txe2x86x92R conformational change. Thus, the reactivity of B3Asn is much lower in the R-state (when the residue resides in an xcex1-helix) than in the T-state.
The interconversion between T6, T3R3 and R6 conformations of the two zinc insulin hexamer is modulated by ligand binding to the T3R3 and R6 forms. Anions such as chloride have affinity for the fourth coordination position in the metal ions of T3R3 and R6, while preservatives such as phenol binds to hydrophobic pockets located near the surfaces of the T3R3 and R6 forms (Derewenda, Nature 338, 594, 1989 and, Brzovic, Biochemistry 33, 130557, 1994). By the use of Co2+ insulin it has been shown that the combined effect of anion and phenol binding is particularly efficient in stabilising the R6 state. (Brader, Trends Biochem. Sci. 30, 6636, 1991 and; Bloom, J. Mol. Biol. 245, 324, 1995). Furthermore, for both Zn2+- and Co2+ insulin it has been shown that phenol is much more efficient than m-cresol in inducing R-state in the insulin hexamer (Wollmer, Biol. Chem. Hoppe-Seyler 368, 903, 1987 and, Choi, Biochemistry 32, 11638, 1993). High affinity phenol derivatives inducing R-state are 7-hydroxy-indol ((Dodson, Phil. Trans. R. Soc. Lond. A 345, 153, 1993) resorcinol and 2,6- and 2,7-dihydroxy-naphtalen ((Bloom, J. Mol. Biol. 245, 324, 1995).
The physical denaturation of insulin is known as fibrillation. In the fibrillar state extended peptide chains are laying parallel or anti parallel and hydrogen bonded to each other, so-called xcex2-structure or xcex2-pleated sheets. Fibrils represent usually the lowest state of energy of the protein, and only harsh conditions such as strong base may enable a regeneration from this state to the native state of correctly folded protein. Factors that promote the rate of formation of fibrils are increasing the temperature, increasing the surface area between the liquid and the air phase and, for zinc-free insulin, increasing the concentration. For hexameric zinc-insulin the rate of fibril formation decreases with increasing concentration. The formation of fibrils is believed to proceed via monomerization of insulin. Fibrils of insulin have the appearance of gels or precipitates.
Insulin derivatives having truncations in the C-terminal of the B-chain, e.g. des-pentapeptide (B26-B30) insulin and des-octapeptide (B23-B30) insulin are more prone to form fibrils than human insulin. Insulin analogues which dissociate readily from the hexameric unit to the monomeric form, e.g. the AspB28 human insulin and the LysB28-ProB29 human insulin, are likewise more prone to form fibrils than human insulin.
The native state of insulin is stabilised by bringing about the conditions that stabilises the hexameric unit, i.e. the presence of zinc ions (2-4 zinc/hexamer), phenol (0.1-0.5% w/v) and sodium chloride (5-150 mM).
Addition of agents that reduce the surface tension at the air-liquid interface further reduces the propensity to fibril formation. Thus, polyethylene glycol, polypropylene glycol and co-polymers hereof with an average molecular weights of about 1800 have found use as stabilisers in concentrated insulin solutions for infusion pumps (Grau, 1982. In: Neue Insuline (Eds. Petersen, Schlxc3xcter and Kerp), Freiburger Graphische Betriebe, pp. 411-419 and Thurow,1981: patent No. DE2952119A1). For a comprehensive review on the physical stability of insulin see Brange 1994, Stability of Insulin, Kluwer Academic Publisher, pp. 18-23.
Most of the chemical degradation of insulin in preparations is due to reactions involving the carboxamide function of the asparagine residues, in particular residues B3 and A21. Hydrolysis of the amide groups leads to desamido derivatives, and transamidation involving an amino group from another molecule leads to covalently linked dimers and, after similar consecutive reactions, to trimers and higher polymers.
In acid solution AsnA21 is the most reactive, leading to AspA21 insulin (Sundby, J. Biol. Chem. 237, 3406, 1962). In crude insulin of bovine and porcine origin, obtained by acid ethanol extraction, the most abundant dimers isolated were AspA21-GlyA1 and AspA21-PheB1 linked (Helbig 1976, Insulindimere aus der B-Komponente von Insulinprxc3xa4parationen, Thesis at the Rheinisch-Westfxc3xa4lischen Technischen Hochschule, Aachen).
In neutral solution, which is the preferred embodiment of insulin preparations for injection therapy, AsnB3 is the most susceptible residue. Degradation products include AspB3 insulin, AspB3-GlnB4 isopeptide insulin, and dimers and higher polymers where AspB3 provides the carbonyl moiety of a peptide bond with an amino group of another molecule. For a comprehensive review on the chemical stability of insulin see Brange 1994, Stability of Insulin, Kluwer Academic Publisher, pp. 23-36. As for the physical stability conditions that stabilises the hexameric unit, i.e. the presence of zinc ions (2-4 zinc/hexamer), phenol (0.1-0.5% w/v) and sodium chloride (5-150 mM), decrease the rate of formation of degradation products during storage at neutral pH.
A different type of polymerisation reaction is observed when the conditions that stabilises the hexameric unit is neglected. Thus, in the absence of zinc, phenol and sodium chloride, and using a temperature of 50xc2x0 C., disulfide-linked dimers and high molecular weight polymers are the prevailing products formed. The mechanism of formation is a disulfide interchange reaction, resulting from xcex2-elimination of the disulfides (Brems, Protein Engineering 5, 519, 1992).
Solubility of insulin is a function of pH, metal ion concentration, ion strength, phenolic substances, solvent composition (polyols, ethanol and other solvents), purity, and species (bovine, porcine, human, other analogues). For a review see Brange: Galenics of Insulin, Springer-Verlag 1987, p.18 and 46.
The solubility of insulin is low at pH values near its isoelectric pH, i.e. in the pH range 4.0-7.0. Highly concentrated solutions of porcine insulin (5000 U/mlxcx9c30 mM) have been brought about at acid pH (Galloway, Diabetes Care 4, 366, 1981), but the insulin in the formulation is highly instable due to deamidation at AsnA21. At neutral pH highly concentrated solutions of zinc free insulin can be made, but these are unstable due to a high rate of polymerisation and deamidation at AsnB3. Porcine zinc insulin solutions at neutral pH comprising phenol have been reported physical stable at concentrations of 1000 U/ml at elevated temperature, but become supersaturated when the temperature is lowered to 4xc2x0 C. (Brange and Havelund in Artificial Systems for Insulin Delivery, Brunetti et al. eds, Raven Press 1983).
In order to reduce the inconvenience of insulin injections much attention has been given to alternative routes of administration (for an overview see Brange and Langkjaer in Protein Delivery: Physical Systems, Sanders and Hendren, eds., Plenum Press 1997). Pulmonary delivery seems to be the most promising of these (Service, Science 277, 1199, 1997). Insulin can be given aerolised in the form of dry powder or as nebulised droplets from an insulin solution. The efficacy might be enhanced by coached breathing (Gonda, U.S. Pat. No. 5,743,250) and addition of an absorption enhancer (Baekstroem, U.S. Pat. No. 5,747,445) or protease inhibitors (Okumura, Int. J. Pharm. 88, 63, 1992).
The bioavailability of a nebulised concentrated insulin solution (500 U/ml) was shown to be 20-25% as compared to a subcutaneous injection (Elliot, Aust. Paediatr. J. 23, 293, 1987). By using 30-50 xcexcl insulin solution per puff the insulin solution need to be 5-20 times more concentrated than the usual concentration of 0.6 mM. By using a single dose container, e.g. a blister pack (Gonda, U.S. Pat. No. 5,743,250), the demand for a preservative is abolished. Most insulin formulations are preserved by the toxic, mucose irritating and unpleasant odorous phenol and m-cresol. However, omitting phenols will cause stability problems. In addition to the bacteriostatic efficacy, the phenols act as physico-chemical stabilisers of insulin in combination with zinc ions. So, it is preferred that formulations of insulin for inhalation are made with a minimum concentration of phenol or that phenol has been replaced by more acceptable substitutes.
Definitions
By xe2x80x9canalogue of human insulinxe2x80x9d (and similar expressions) as used herein is meant human insulin in which one or more amino acids have been deleted and/or replaced by other amino acids, including non-codeable amino acids, or human insulin comprising additional amino acids, i.e. more than 51 amino acids.
By xe2x80x9cderivative of human insulinxe2x80x9d (and similar expressions) as used herein is meant human insulin or an analogue thereof in which at least one organic substituent is bound to one or more of the amino acids.
By xe2x80x9cnon-phenolic substancexe2x80x9d is meant an organic compounds which does not contain a structural fragment consisting of a benzene ring to which a hydroxy group is bound.
By xe2x80x9cstabiliserxe2x80x9d is meant a substance which acts like phenol and m-cresol by inducing the R6 conformation of the two zinc insulin hexamer.
By xe2x80x9cphenol mimicxe2x80x9d is meant a non-phenolic substance which is capable of inducing the R6 conformation of the two zinc insulin hexamer.
It is an object of the present invention to provide a stable insulin formulation which is useable for pulmonary delivery, and which has an increased convenience for the patient without deteriorating the physical and chemical stability.
Furthermore, it is an object of the invention to provide a stable insulin formulation for delivery, when the presence of phenol and m-cresol are undesirable, in single dose containers without a preservative or in multiple dose containers with other preservatives.
These objects have unexpectedly been accomplished by providing an insulin formulation in which phenol and m-cresol, commonly used in insulin formulations, have been replaced with a non-phenolic substance which acts like phenol and m-cresol by inducing the R6conformation of the two zinc insulin hexamer. These compounds are subsequently named stabilisers.
Unexpectedly, such stabilisers have been found among the non-toxic and pleasant odorous or non-odorous substances selected from the group of monoterpenes, especially bicyclic monoterpenols as borneol and isopinocampheol, tricyclic aliphatic alcohols as 1-adamantanol and purines as purin and adenine.
Accordingly, the present invention relates to an aqueous insulin formulation comprising: human insulin or an analogue or a derivative thereof, zinc ions and a non-phenolic stabiliser which is capable of inducing the R6 conformation of the two zinc insulin hexamer.
Furthermore, the stabilisers provided by the present invention may be used in insulin solutions for pump treatment or for injection without addition of a preservative or in combination with other preservatives than phenol and m-cresol.
Preferred Embodiments
The non-phenolic stabiliser is preferably selected from the group consisting of bi- or tricyclic aliphatic alcohols and purines.
In a preferred embodiment the non-phenolic stabiliser is a bicyclic aliphatic alcohol, preferably a monoterpenol, more preferably isopinocampheol, 2,3-pinandiol, myrtanol, borneol, norborneol or fenchol.
In another preferred embodiment the non-phenolic stabiliser is a tricyclic aliphatic alcohol, preferably 1-adamantanol.
In another preferred embodiment the non-phenolic stabiliser is a purine, preferably purine, adenine, guanine or hypoxanthine.
All of the above mentioned non-phenolic stabiliser have been found to be non-toxic and pleasant odorous or non odorous.
The insulin formulation preferably comprises at least 3 molecules of said non-phenolic stabiliser per six molecules of insulin, preferably up to 50 mM of said non-phenolic substance.
The insulin formulation preferably contains 0.3 to 20 mM, preferably 0.6 to 15 mM, more preferably 3 to 15 mM of human insulin or an analogue or a derivative thereof.
The stability of the insulin formulation is further improved when the concentration of chloride is kept below 50 mM, preferably below 30 mM, and more preferably in the range of 5 to 20 mM.
A remarkable stability of the insulin formulation is obtained when it comprises less than 10 mM of any anions other than chloride and acetate.
In a particular embodiment the insulin may comprise a low amount of phosphate buffer, preferably up to 5 mM of phosphate.
Insulin formulations of the invention comprising 2.0 to 4.5 Zn2+ ions, preferably 2.5 to 3.5 Zn2+ ions per six molecules of insulin, are very stable.
In an alternative embodiment, the insulin formulation of the invention comprises 2.5 to 4.5 Zn2+ ions, preferably 3 to 4 Zn2+ ions per six molecules of insulin.
Surprisingly, it is possible to add a relatively high concentrations of zwitterions such as glycylglycine and glycine to the insulin formulation of the invention without decreasing the solubility of insulin. Glycylglycine act as buffer at neutral pH and furthermore increase the dissolution rate of zinc insulin at neutral to basic pH due to a moderately zinc chelating effect. Also, glycylglycine may act as a scavenger for amine reactions during the storage time. Thus, in a preferred embodiment the insulin formulation of the invention further comprises 5 to 150 mM of a zwitterionic amine, preferably glycylglycine or glycine.
In another preferred embodiment the insulin formulation comprises a zwitterionic amine selected from the group consisting of BICINE, TRICINE and BIS-TRIS.
In another preferred embodiment the insulin formulation comprises a zwitterionic amine selected from Good""s buffers.
In a preferred embodiment the insulin formulation of the invention further comprises 5 to 50 mM of trishydroxymethylaminomethan, which acts as a buffer at neutral pH and as a scavenger for amine reactive compounds.
In another preferred embodiment the insulin formulation of the invention comprises between 0.001% by weight and 1% by weight of a non-ionic surfactant, preferably Tween 20 or Poloxamer 188. A nonionic detergent can be added to stabilise insulin against fibrillation during storage and nebulisation.
In a preferred embodiment the insulin used is human insulin.
In another preferred embodiment the insulin used is an analogue of human insulin wherein position B28 is Asp, Lys, Leu, Val or Ala and position B29 is Lys or Pro; or des(B28-B30), des(B27) or des(B30) human insulin.
The preferred analogues of human insulin are those in which position B28 is Asp or Lys, and position B29 is Lys or Pro, preferably AspB28 human insulin or LysB28ProB29 human insulin.
The insulin analogue can also be selected among those disclosed generically as well as specifically in EP 885 961 (such as (B3)Lys, (B28)lle, (A21)Gly human insulin).
In another preferred embodiment the insulin is selected from the group of soluble long-acting insulin derivatives such as derivatives of human insulin having one or more lipophilic substituents, preferably acylated insulins.
The insulin derivative according to this embodiment is preferably selected from the group consisting of B29-Nxcex5-myristoyl-des(B30) human insulin, B29-Nxcex5-palmitoyl-des(B30) human insulin, B29-Nxcex5-myristoyl human insulin, B29-Nxcex5-palmitoyl human insulin, B28-Nxcex5-myristoyl LysB28 ProB29 human insulin, B28-Nxcex5-palmitoyl LysB28 ProB29 human insulin, B30-Nxcex5-myristoyl -ThrB29LysB30 human insulin, B30-Nxcex5-palmitoyl-ThrB29LysB30 human insulin, B29-Nxcex5-(N-palmitoyl -xcex3-glutamyl)-des(B30) human insulin, B29-Nxcex5-(N-lithocholyl-xcex3-glutamyl)-des(B30) human insulin, B29-Nxcex5-(xcfx89-carboxyheptadecanoyl)-des(B30) human insulin and B29-Nxcex5-(xcfx89-carboxyheptadecanoyl) human insulin.
The most preferred insulin derivative is B29-Nxcex5-myristoyl-des(B30) human insulin or B29-Nxcex5-(N-lithocholyl-xcex3-glutamyl)-des(B30) human insulin.
The above mentioned soluble long acting insulin derivatives bind albumin and have been designed to provide a constant basal supply of insulin (Markussen, Diabetologia 39, 281, 1996). Subcutaneous administration once or twice daily secure the required basal delivery of insulin, whereas several daily inhalations are recommended using pulmonary administration, preferably in connection with meals.
The insulin derivatives have a protracted onset of action and may thus compensate the very rapid increase in plasma insulin normally associated with pulmonary administration. By careful selection of the type of insulin, the present invention enables adjustment of the timing, and in order to obtain the desired insulin profile.
In a particular embodiment of the present invention, the insulin formulation comprises an insulin analogue or human insulin as well as an insulin derivative.
The insulin preparation of the present invention preferably has a pH value in the range of 7 to 8.5, more preferably 7.4 to 7.9.
The present invention also relates to a method of treating type I or type II diabetes, comprising administering (preferably by pulmonary delivery) to a patient in need of such treatment an insulin formulation according to any of the preceding claims.
In a preferred embodiment, insulin formulation is administered in connection with meals.